The output voltage of an electric power converter in a controller for controlling current supplied to an AC motor by vector control may be limited (saturated). Prior art applicable to this case is described in, for example, Japanese Patent Laid-open No. 2004-180441. Specifically, to prevent the AC motor from generating an overcurrent, a current command for the q-axis in the d-q coordinate system, which is an orthogonal rotational coordinate system, is corrected so that current Id in the d-axis direction becomes 0 and an interfering item of the q-axis, which interferes with the d-axis, is operated.